Storage and retrieval machines are commonly used in material and inventory storage facilities for storing items in and retrieving the items from the facilities. Typical of such facilities are warehouses having storage racks of substantial height and width arranged along aisles in which the storage and retrieval machines travel on rails to various rack locations. Due to the need to have a highly efficient storage facility, the storage racks are designed to provide a maximum number of rack storage locations in both height and width directions.
The storage and retrieval machines are typically self-propelled by electric drive motors and operate continuously and automatically at the direction of a control system including control components located both on the storage and retrieval machine and remote from the machine. Storage and retrieval machines typically have a continuous very high duty usage which subjects them to a high level of wear which frequently is not monitored and promptly corrected, particularly due to the continuous and automatic operation of the machine from remote control locations. One of the major areas of wear is that of the base wheels and wheel bearings. The wear of the wheels and their bearings is particularly exacerbated when the wheels roll at a skew angle relative to the rails. Running the storage and retrieval machine in the direction of the rail while the wheels are rolling at a skew angle relative to the rail causes wear of the wheels and rail surface as well as placing a high thrust load on the wheel bearings causing their deterioration.
The ability to easily position rails on storage and retrieval machines in alignment and without skew relative to the supporting rail and to reliably hold the wheels in the correct position is critical to avoid rapid, substantial wear on the wheels. Presently known positioning devices do not provide easy position adjustment and reliable holding of the wheel position, and frequently the wheel bearing, support frame and positioning mechanism of present wheel holding devices occupies a substantial amount of space requiring enlargement of the entire base to which the wheels are affixed. An example of one present approach to wheel support which is used to align the wheels with a rail is the provision of separate adjustment mechanisms for each of the two pillow blocks supporting each end of a wheel axle. Because of the need to provide access to hold the bearings and their races in place, the wheel positioning mechanism cannot be located where it is most effective in holding the pillow blocks properly positioned. Also, providing space for access to the bearings as well as space for the position adjustment mechanism results in an undesirable lengthening of the base on which the wheel is mounted.